A number of recombinant clones expressing surface componetns of Chlamydia trachomatis and C. psittaci have been characterized during the last year. One set of recombinants, expressing the genus-specific lipopolysaccharide (LPS) of Chlamydia, contains an insert of C. trachomatis serovar L2 DNA. The original recombinant has been extensively manipulted in order to surmise the nature of the recombinant polypeptide product and to facilitate the sub-cloning of the gene into a variety of cloning vectors. Enteric bacteria with well-characterized LPS structures have been transformed with recombinant plasmids harboring the genes which direct the synthesis of the chlamydial LPS-epitope; LPS from these strains have been analyzed structurally to determine the components of the epitope. New recombinant clones from C. trachomatis serovars L2 and B have been isolated that contain genes encoding the major outer membrane protein (MOMP). Expression of the entire MOMP is apparently lethal for Escherichia coli since we are unable to subclone the entire gene into expression vectors. However, expression of MOMP epitopes has been obtained by fusing portions of the MOMP gene to Beta-galactosidase using lambda gt11 as a cloning vector. We have found reiterated sequence in or next to the MOMP gene in the B-serovar genome. Another set of recombinants has been indentified that expresses a number of surface components of the B-serovar of C. trachomatis, including three recombinants that express putative adhesions porteins of C. trachomatis.